The present invention relates to a temperature sensor based upon an optical interferometer which is constructed from single mode optical fibre and in which the detection and measurement of temperature is based upon optical interference or fringe patterns. More particularly, it relates to such a temperature sensor based on an all fibre Michelson interferometer which can be operated remotely from sources of power or light generation and is connected to such sources by optical fibres.
The measurement of temperature in an industrial environment is usually achieved using well-established transducers such as platinum resistance thermometers, thermocouples or bi-metallic strips. Although these transducers have become industry standards it has become evident that there is a demand for new types of thermometers for special applications where electrically based transducers cannot operate for reasons of safety or the presence of noisy electrical environments. Some of the potential applications of optical fibre thermometry are in the measurement of temperature in for example jet engines, nuclear reactors, and transformers. A fibre optic thermometer could also be used in the treatment of cancer where the tumour is subjected to microwave radiation which consequently eliminates the use of any of the conventional electronic sensors.
Optical phase modulation sensors offer the highest resolution of all optical displacement sensors; for example, classical interferometers of the Michelson or Mach Zehnder type can be used to detect displacements as small as 10.sup.-14 m. Although interferometers offer tremendous resolution (or sensitivity) until recently very little effort had been devoted to developing them into general purpose displacement sensors. This is primarily because the sensitivity of an interferometer is a function of the relative alignment of the optical beams, and in a typical interferometer where beam splitters and mirrors are used to control the amplitude division and recombination of the light the sensitivity will fluctuate if the optical components are randomly disturbed. However, the recent introduction of all fibre interferometers has virtually eliminated this problem as the alignment of the fibre guided optical beams is virtually immune from mechanical disturbance.